The present application relates to the art of medical diagnostic imaging in which penetrating radiation is received by radiation sensitive detectors. The application subject matter finds particular use in computerized tomographic (CT) scanners and will be described with particular reference thereto. However, the invention may also find use in connection with other diagnostic imaging modalities, industrial quality assurance imaging, video camera imaging, and the like.
Heretofore, CT scanners have included a plurality of discrete radiation detectors which converted X-ray radiation which traversed a patient examination area into electronic signals. Each radiation detector included a radiation sensitive face, such as a scintillation crystal, which converted the received radiation into a corresponding quantity of light. A solid state photodiode was provided to convert the light emitted by the scintillation crystal into analog electrical signals indicative of the intensity of the crystal emitted light, hence the intensity of the received radiation.
The radiation detectors were separately arranged on a circuit board. Each circuit board supported a linear array of photodiodes and attached scintillation crystals. In addition, a preamplifier was attached to the circuit board and connected to each photodetector output to convert the photodiode current to an appropriate voltage within the dynamic range of the analog-to-digital conversion system.
The analog signals from the circuit board were carried to a central processing area where they were converted from their analog state into a corresponding digital signal. The analog signals were carried to the central processing area via a long bus system which extended around the scanner.
One problem relates to degradation of the analog signals as they travel over the long bus system between the radiation detectors and the central processing area.
CT scanners operate in a sea of extraneous radio frequency electromagnetic signals, the frequencies of which vary over a wide band. Sources of extraneous signals include nearby operating electrical components, equipment, signals from other detectors, and the like. The long bus systems include long lead wires which inadvertently act as antennas in picking up extraneous electromagnetic signals and converting them into analog signals. The extraneous analog signals are superimposed on and mix with the analog signals from the detectors. The superimposed extraneous signals appear as noise and fictitious data when reconstructed into images. The resulting images are degraded by noise, ghosting, and other artifacts.
Prior art scanners commonly collected data from a single slice or a small plurality of slices. To scan a volume, the patient was shifted longitudinally either incrementally after each slice to generate a multiplicity of parallel slices or continuously for a helical scan. The multiple rotation of the x-ray beam around the subject was time-consuming and stressful on the x-ray tube and generator.